The present invention relates to connectivity between land-based cellular communications systems and mobile cellular communications equipment located in air-borne craft, and more particular to cell selection by mobile cellular communications equipment while airborne.
The world is becoming more and more connected, and this has led consumers to have increasing expectations of being able to be online and experience at least moderate data rates regardless of time and location. As one response to these expectations, the next generation of mobile technology, the so-called IMT-2020 (5G), targets high-speed mobility as one objective. The exemplary scenarios studied are high-speed trains and vehicles on freeways, but following the recent trend, it is expected that terrestrial in-flight broadband service for airplanes will be in the scope—either as direct communication between the User Equipment (UE) and base station, or via an access point (AP) onboard the aircraft which aggregates the traffic of some number of UEs and maintains a link to the base station.
In 2013 the Federal Communications Commission (FCC) took steps towards enabling better connectivity by assigning a 500 MHz wide subband in the 14 GHz radiofrequency (RF) band for in-flight air-to-ground broadband connection. The FCC's expectation is that by year 2021 there will be a demand for 15000 flights offering high-speed broadband connectivity to its passengers. By comparison, the availability in year 2013 was 3000 airplanes world-wide, and this was with connections that were deemed too slow and by far too expensive by consumers. The industry has noted that today's airline passengers expect the same level of broadband service that is available on the ground.
Several trials have been carried out offering terrestrial network coverage in lower frequency bands typically used for regular cellular networks. Recent advances on the regulatory side of aviation will, if properly exploited, greatly enhance and simplify in-flight broadband services that are based on terrestrial networks.
The principles for maintaining coverage for mobile communication equipment on the ground are well known. So-called radio base stations are deployed at various geographical positions, and for a given mobile communication equipment, a “best-suited” base station is selected as the point of connection into the communications system. As the mobile communication equipment changes its position, the quality of its radio connection with the serving base station may deteriorate to the extent that a reselection is made, whereby a better-suited base station takes over as the serving base station.
It can be seen that in conventional telecommunications systems, which focus on communication with mobile devices on the ground, the deployment of base stations is designed to provide single macro cell coverage at each geographical position (except, of course, at cell edges where handovers of service occur from one base station to another). In order to achieve cost efficient communication with communication equipment aboard aircraft in the sky, it is desirable to reuse the macro grid of existing telecommunications systems for that communication. However, such reuse is not a straightforward matter because the existing strategies used for cell selection and reselection by mobile equipment on the ground are not useful when that equipment is airborne. The reason is that cell selection on the ground relies substantially on signal measurements related to path loss, and on the ground this is essentially related to geography because, for example, buildings and terrain make it a richly scattering environment. In most circumstances, the best-suited macro cell for equipment on the ground will be the one that the mobile communications equipment is physically closest to.
But in the air, line of sight (LoS) conditions prevail—there are essentially no surrounding scatterers—and as a result the signals received from a number of base stations all have approximately the same path loss. Thus, the signal measurements and strategies that are typically used for cell selection/reselection in existing systems are not useful when applied to airborne equipment.
Hence there is a need for technology that allows airborne mobile communication equipment to select/reselect a serving cell from among a number of potential base stations deployed on the ground at geographically diverse locations.